Kindly refer to the following link(s):
What is the correct way of holding the tashahhud finger?
Moving the finger during tashahhud
Does moving the finger in Tashahhud hit Shaytan with an Iron Rod?
This is an issue related to the sciences of Hadeeth that only experts can understand it, while layman who are not qualified won’t be able to
If there are 2 strong opinions interchange between them (moving index finger in tashahhud)